Tuned resonance muffler



Dec. 3, 1968 L. ANDERSSON TUNED RESONANCE MUFFLER 2 Sheets-Sheet 1 Filed April 11. 1966 INVENTOR Lou'as Adam l-hk 444 3, 1968 1.. ANDERSSON 3,414,073

TUNED RESONANCE MUFFLER Filed April-ll, 1966 2 Sheets-Sheet 2 INVENTOR bans Ruins) BY W114;

United States Patent 3,414,078 TUNED RESONANCE MUFFLER Louis Andersson, Gotgatan 73, Stockholm, Sweden Filed Apr. 11, 1966, Ser. No. 541,607 Claims priority, application Switzerland, Mar. 15, 1966, 3,7 12/ 66 8 Claims. (Cl. 181-48) ABSTRACT OF THE DISCLOSURE A sound mufiler for combustion engines is disclosed. The sound muffier comprises an elongated hollow casing having an inner tube concentrically mounted therein, a portion of the inner tube extending into the hollow casing and a portion of the inner tube extending outside the hollow casing past the rear end thereof. The portion of the inner tube extending into the hollow casing terminates within the hollow casing at a location approximately equal to one half the total length of the hollow casing at approximately the location of a node of a standing wave generated therein. A ring member is provided for sealing the rear end of the hollow casing about the inner tube whereby an annular intermediate compartment is formed between the inner tube and the hollow casing. The relative positioning and dimensions of the hollow casing and the inner tube are such that sound is dampened as efficiently as possible and, at the same time, as small resistance as possible exists opposing the departing exhaust gases.

The present invention relates to an improved sound mufiler for combustion engines.

One problem associated with sound mufflers is that they should dampen as efficiently as possible the sound produced by the escaping exhaust gases and, at the same time, as small resistance as possible should oppose the departing gases. Large gas resistance unfavorably influences engine efliciency.

This problem is most effectively solved by the present invention through the provision of a new and improved construction of sound muffler incorporating a hollow casing and an internal tube open at both ends located in said casing. The formed annulus or ring-shaped intermediate compartment is sealed between the end of the casing and the internal tube by a ring member. The length of the casing is selected such that there occurs a standing sound wave and the internal tube terminates at least approximately at a node.

It has been found that the efliciency of an engine or combustion power plant can be improved with such type sound muffler and, at the same time, it is possible to also improve dampening of the sound energy with respect to standard mufflers.

Accordingly, it is a primary object of the present invention to provide an improved sound muffler which effectively dampens sound.

Another, more specific object of this invention concerns itself with an improved muffler, particularly for combustion engines, which is extremely effective in dampening sound energy, relatively inexpensive and uncomplicated in construction, easy to mount and service, and increases the efficiency of the combustion engine.

Still a further important object of this invention pertains to an improved construction of sound muffler for a combustion power plant which reliably dampens sound energy while providing minimum flow resistance to the escaping gases.

Other features, objects and advantages of the invention will become apparent by reference to the following detailed description and drawings in which:

FIGURE 1 is a schematic front view, partly in crosssection, of a preferred embodiment of inventive muffler;

3,414,078 Patented Dec. 3, 1968 FIGURE 2 is an enlarged, fragmentary cross-sectional view of the rear end of the mufiler of FIGURE 1; and

FIGURE 3 schematically illustrates a sound wave for purposes of theoretically explaining the mode of operation of the inventive muffler.

Describing now the exemplary embodiment of inventive sound mufiler depicted in FIGURES 1 and 2, it will be recognized that such incorporates a metallic hollow casing or tubular shell 1 having a curved portion 3 connected via a connecting piece or stud 5 with a non-illustrated combustion engine. Internally of this hollow casing 1 there is located an inner open-ended tube or pipe 2 of smaller diameter, so that an annulus or ring-shaped intermediate compartment 7 is formed between the aforesaid casing 1 and the inner tube 2. Annulus or ring-shaped intermediate compartment 7 has the same, constant radial width all around due to the coaxial arrangement of outer casing 1 and inner tube 2. A fixedly mounted or annular disk or ring member 9 tightly seals the rear end 1a of the casing 1. Connection of such sealing ring or disk 9 to the rear end 1a of the casing 1 and the outer surface of the inner tube 2 can be performed by welding 11 for instance.

It will also be observed that, in the depicted embodiment, the inner tube 2 has a short tail piece 6 which extends past the rear end In of the casing 1. Inner tube 2 is supported at the casing 1 at the region of its forward end 10 by any suitable means, such as narrow holding webs or arms 4 in such manner that the free cross-section is only insignificantly reduced at this location. This inner tube 2, which is open at both ends, has an internal cylindrical compartment 8, the cross-sectional area of which is preferably half of that of the casing 1. According to an important aspect of the invention, the length of the casing 1 must be selected such that there is generated a standing wave.

It is also important how far the inner tube 2 extends into the hollow casing 1 in order to obtain good sound dampening. Such is then possible if the inner tube 1 terminates at a node of the standing wave. The distance A through which the inner tube 2 extends into the hollow casing 1 amounts to about one-half of the so-called straightened length or distance from the rear end In of the casing 1 to the valves or valve seats of the engine. Under the term straightened length or distance as used herein there is to be understood the actual length of a member as measured. between two reference points and substantially along the central lengthwise axis thereof. The forward end 10 of the inner tube 2 therefore terminates at a node, designated by reference character E in FIGURE 3. What is believed to be the theoretical explanation for the surprisingly good sound dampening obtained with the inventive muffler is that the waves are reflected by the ring or disk 9 and since they have the same wave length but opposite pressure distribution along the axis of the tube they will tend to mutually cancel one another or at least considerably weaken one another.

It has been empirically found that the sound waves produced by a four or six cylinder four-stroke gasoline engine possess a wave length B of approximately 4.8 meters. Half a wave length C is then, of course, approximately 2.4 meters. The casing 1 including connecting joints or the like up to the valves or valve seats of the engine should possess such length in order to obtain as favorable as possible sound-dampening action.

Further, it has been found that for the gas wave length of 610 millimeters must be assumed. Therefore, half the wave length amounts to 305 millimeters. A further aspect of the invention is to construct the total length A- of the inner tube 2 extending into the hollow casing 1 such that it amounts to a multiple of the half wave length, preferably a multiple of the wave length, in the present case then 1.22. meters. In so doing, the inner tube 2 has a short piece 6 extending somewhat past the casing 1, namely one to six centimeters. Thus, it is possible to obtain resonance and to keep the gas resistance extremely small. To regulate the optimum value it is advantageous to provide the rear end 6 of the inner tube 2 with a telescopically displaceable sleeve, as such has been depicted by the sleeve 12 shown in phantom lines in FIGURE 2. This sleeve 12 can, if desired, be manually displaced from the interior of the vehicle or even automatically as a function of the vehicle speed or other engine parameters so that optimum results are realized. In order to obtain good sound dampening and at the same time small gas resistance, the cross-sectional area of the inner tube 2 should not be greater than 60% or less than 30% of the cross-sectional area of the casing 1.

In a practical structural manifestation of the present invention, the following dimensions have proven themselves to be advantageous: length of the casing up to the valves=2.4 meters; length of the inner tube internally of the casing=l.24 meters; length of the free rear pipe end=2-4 centimeters; inner diameter of the casing=84 millimeters; inner diameter of the inner tube=50 millimeters. Suitable material for the previous components can be sheet iron or rustproof sheet metal.

Apart from use with motor vehicles, the inventive mufller could also find utility in stationary machines or airplanes. Furthermore, it would be possible to make the inner tube 2 telescopically displaceable within limits at the disk 9.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practised within the scope of the following claims.

What is claimed is:

1. A sound muffier for combustion engines, comprising an outer tube, an inner tube open at both ends located within said outer tube, said outer tube and inner tube forming therebetween an elongated annular intermediate chamber, said outer tube having a front end adapted to be coupled to the engine and a rear end, a ring member disposed at said rear end for sealing said annular intermediate chamber, said outer tube having at least a curved portion at the region of its front end, said inner tube including a portion extending past said rear end of said outer tube and opening directly into the atmosphere, the length of the remaining portion of the inner tube extending internally of said outer tube and measured from said ring member inwardly towards said front end amounting to about /2 to /3 of the straightened axial length of said outer tube, said intermediate annular chamber having along its entire length a substantially constant crosssection, and supporting means located between said inner and outer tubes to hold said inner tube in substantially coaxial position in said outer tube without significantly reducing the cross-section at this location.

2. Sound mufiler as defined in claim 1, wherein the cross-sectional area of the inner tube amounts to less than 60% of the cross-sectional area of the outer tube.

3. Sound muffler as defined in claim 1, wherein said outer tube possesses about twice the cross-sectional area at the region where said inner tube terminates than the cross-sectional area of said inner tube.

4. Sound muffler as defined in claim 1, wherein said inner tube extends into the outer tube approximately to the middle of the spacing between the front end of the outer tube and the rear end of the outer tube as measured substantially along the central, lengthwise axis of said outer tube.

5. The combination defined in claim 4, wherein said hollow casing includes a connecting piece, the straightened length of said hollow casing together with said connecting piece measured up to the valve seats of the engine amounts to 230 to 250 centimeters.

6. Sound muffler as defined in claim 4, wherein said inner tube includes a portion extending past the rear end of the outer tube, said portion being constructed as a telescopically displaceable member the effective length of which can be altered.

7. Sound mufiler for combustion engines as defined in claim 6, wherein said outer tube possesses a cross-sectional area which is less than three times the cross-sectional area of the inner tube, and wherein said supporting means are located between said inner and outer tubes at the region of the end of said inner tube remote from said externally extending portion.

8. A sound mufiler for a combustion engine having valves and valve seats, said sound mufiler comprising: an elongated hollow casing of substantially constant circular cross-section, said casing having a forward end adapted to be coupled tothe valves and valve seats of the combustion engine, and a rear end; an inner tube of substantially constant circular cross-section open at both ends thereof, said inner tube extending into said hollow casing from the rear end of said hollow casing, a distance approximately equal to half the length of said hollow casing to terminate substantially at a standing wave node, a portion of said inner tube extending outside said hollow casing past the rear end thereof, the cross-sectional area of said inner tube being less than 60% of the cross-sectional area of said hollow casing; web means for concentrically mounting said inner tube in said hollow casing at the region of the forward terminating end of said inner tube; and ring means located at said rear end of said hollow casing for closing said rear end about said inner tube.

References Cited UNITED STATES PATENTS 1,601,884 10/1926 Rylsky 18164 1,910,672 5/1933 Bourne 18148 2,075,265 3/ 1937 Bourne 18159 2,099,887 11/1937 Heath l8133 2,297,046 9/1942 Bourne 181-48 2,305,946 12/1942 Wilson et a1. 18133 3,263,772 8/1966 Irwin et a1. 181-59 3,338,331 8/1967 Jettinghotf -181-48 XR 3,348,629 10/1967 Cassel 181-48 FOREIGN PATENTS 707,697 6/ 1941 Germany.

484,771 5/1938 Great Britain.

487,816 6/1938 Great Britain.

742,529 12/ 1955 Great Britain.

751,881 7/ 1956 Great Britain.

OTHER REFERENCES Automobile Engineer: January 1955 issue, pp. 39 and 40.

ROBERT S. WARD Ir., Primary Examiner. 

